1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device including a laser chip, and more particularly to a method of manufacturing a semiconductor device, including a process for cleaning off an adherent such as an organic material.
2. Description of the Related Art
For convenience of operation, an adhesive sheet containing an organic material has been heretofore used to manufacture a semiconductor device using a semiconductor laser. For example, a dicing process for cutting separate laser chips out of a wafer involves cutting the wafer on the front side thereof with a dicing saw after previously sticking an adhesive sheet (a so-called dicing tape) on the back side of the wafer in order to hold the laser chips in such a manner that the divided laser chips do not come apart. The separated laser chips, which are bonded to the adhesive sheet, are mounted on a base (a package) by picking up the laser chips one by one. Even during the mounting, the front and back surfaces of each laser chip are covered with the adhesive sheet in order to protect electrodes and the like.
However, the use of the adhesive sheet having the organic material mixed therein in an assembly process causes the adhesion of an adherent on the manufactured semiconductor device. The organic material contained in the adherent volatilizes into the air, and the volatilized organic material chemically reacts with emitted laser light in an atmosphere. As a result, a photo CVD (photo chemical vapor deposition) effect causes the deposition of a material such as a silicon (Si) compound, carbon (C), or an organic material on a laser light emitting edge having the highest optical density. This phenomenon is noticeable, particularly when a nitride semiconductor laser having an oscillation wavelength in or near an ultraviolet region is used in the semiconductor device.
The deposited material causes not only interference with output of laser light but also a change in reflectance of a laser edge. Consequently, an operating current abnormally varies during the driving of a laser, and this may lead to a considerable deterioration in longevity characteristics of the laser.